During the treatment of waste water, one goal is to selectively remove and separate the various solids and dissolved materials from the influent. Waste water treatment systems are used in a number of applications including but not limited to the treatment of sewage, storm water, industrial waste, mining and agriculture. Many prior art waste water treatment systems maintain a continuous flow of influent entering the primary settling tank and effluent exiting the primary settling tank for secondary treatment, resulting in the incomplete removal of grit, solids, and particulates and little if any separation of desirable materials from undesirable materials.
An influent feed system (IFS) to classify and separate particulate matter and solvated materials from an influent stream may include one or more influent feed troughs in fluid communication with a clarification tank, also referred to herein as a settling tank. The influent feed troughs have dimensions such that the fluid level rise rate in an influent feed trough is less than the settling rate of materials to be deposited in the influent feed troughs.
One or more settling tanks are in fluid communication with the one or more influent feed troughs. The one or more settling tanks have dimensions which result in a fluid rise rate in each settling tank that is low relative to the settling rate of materials to be deposited in the one or more settling tanks. In some applications, the settling tank is operated in batch mode with intermittent, influent flow and is substantially emptied between fillings.
Each settling tank includes a hopper bottom for accumulation of the materials to be deposited prior to controlled evacuation and connection to an influent source. The hopper bottom has a drainage pipe and a valve in support of controlled evacuation. The influent stream may be separated into two or more streams and recombined under pressure in the one or more settling tanks.
In yet another prior art embodiment, the influent stream delivery mechanism includes a reservoir which accumulates and stores influent, and may include one or more pumps that pump the influent to the influent feed system, and a signal source which turns the pumps on. Alternatively, the reservoir is elevated relative to the influent feed system and in fluid communication with the influent feed system. A control valve is disposed between the reservoir and the influent feed system. The control valve is configured to deliver the influent stream under a gravity head at a pre-determined and substantially constant flow rate, the control valve opening in response to a signal source to permit influent to traverse under an influence of gravity to the one or more settling tanks. The reservoir may include a holding tower.
In another embodiment, the influent feed system further includes a flow meter that measures a flow rate of fluid wherein the system closes the control valve in response to the flow rate falling below a predetermined rate.
In yet another embodiment, the influent feed system includes one or more screen box assemblies that discharge screened influent (also referred to herein as clarified influent) from each settling tank after separation of solids from the influent stream.
According to another aspect, a settling tank to classify and separate particulate matter and solvated organic materials from an influent stream includes an upper portion and a lower portion. The upper portion has a fluid discharge mechanism, e.g., a floating decanter, and the lower portion is coupled to sludge removal apparatus, e.g., a drainage pipe comprising a valve that controls communication of materials between an influent feed system and the drainage pipe, or a bucket-and-chain drag. One or more of the dimensions of the upper portion and the lower portion causes a fluid rise rate that is low relative to the settling rate of materials to be deposited in the settling tank. A deflection plate is positioned between the upper portion and the lower portion. An influent stream delivery mechanism is configured to deliver the influent stream at a predetermined and substantially constant flow rate, although flow of influent into the settling tank may be intermittent. A hopper accumulates one or more deposited materials. The influent stream is separated into two or more streams. The separated influent is recombined in a turbulent static mixing zone created by delivering the separated influent streams under pressure from two or more opposing pipes.
In one embodiment, the influent feed system includes an apparatus to add one or more coagulants and/or flocculating chemicals to the influent stream before the influent stream enters the one or more settling tanks.
A problem exists in the prior art wherein the settling action of added coagulants and/or flocculating chemicals proceeds relatively slowly and thus causes BOD-containing settling solids to be deposited at various points along the influent flow path. The prior art arrangement wherein the influent stream is divided into two streams and then recombined is intended to cause turbulent mixing of the flocculent-containing streams to encourage faster settling within the settling tank itself.
What is needed in the art is a method and apparatus for producing more rapid and complete static mixing and flocculation within the settling tank.